Senior Tory MPs said last night that the Prime Minister had "seen off" the Ulster Unionists' demands for concessions in the Northern Ireland peace process as their price for voting with the Government.

After a day of horse-trading to stave off defeat, ministers said last night's vote showed that John Major was not in the Unionists' pocket.

Douglas Hurd, the former foreign secretary, said: "We saw them off. They were making all sorts of demands at the last minute. You cannot treat the Prime Minister like that."

There were desperate attempts through the day by ministers to prevent the Ulster Unionists from voting against the Government, which they thought had succeeded, until the division at 10pm. Three Labour MPs were "nodded through" because they were too ill. Julian Critchley, the Tory MP, appeared in a wheelchair.

As the vote approached, the Prime Minister called David Trimble, the leader of the Ulster Unionists, to his private office at the Commons in a last-minute attempt to seal a deal before the vote.

Earlier, Sir Patrick Mayhew, the Secretary of State for Northern Ireland, wrote to the Ulster Unionist MP, Ken Maginnis, to offer a partial concession over plans for elections in Northern Ireland.

The Unionists' vote against the Government came as a shock, but the Government had carefully set about limiting the defections from the Tory benches. In the end, it was that care which was the deciding factor.

The opening speech by Ian Lang, the President of the Board of Trade, seemed lacklustre but it was designed to avoid the bombast of the week before, which had upset some Tory MPs as "over the top". It contained enough acknowledgment that mistakes had been made to sway any waverers.

And the assurances on the future safeguards against Public Interest Immunity certificates were tailor-made for Rupert Allason, the Tory MP for Torbay and author of books about spies.

The Ulster Unionists were angry that the Government was contemplating holding the elections on a single massive constituency for the whole of Northern Ireland, favouring the smaller parties, including Ian Paisley's Democratic Unionist Party, which last night abstained in the vote.

Sir Patrick tried to assure Mr Trimble's official Ulster Unionists that no decision had been reached on the arrangements for the elections. He said it could be made at a meeting of all the parties in "proximity talks" before the elections.

The Unionist leader reported back to his nine-strong team, which met at about 8.15pm in the Commons. They privately rejected the assurances as not enough but refused to tell the Government. They also calculated that if they voted against the Government last night, they could vote for the Government in the confidence motion to underline the importance of their votes over the Government.

A senior Northern Ireland minister said: "They made demands which we would not meet. It's as simple as that."

But Mr Major will seek to avoid any lasting rift. Mr Trimble was at pains to point out that his party's vote against the Government was based on the merits of the Scott inquiry report, rather than a rejection of the draft formula for rescuing the peace process, which is now likely to be unveiled tomorrow at a summit between Mr Major and John Bruton.